This is the classic clutch cylinder failure warning symptom.
I went through two masters and two slave cylinders, the last
three done by the same Audi specialist, before I went to a
clutch specialist that found a bad hydraulic line. Have the
hydraulics inspected thorougly by someone you can trust, and
watch over their shoulder if you can; the Audi specialist
who had three opportunities to do the inspection didn't do
it adequately. All this in the '86 version of the same car.
The Audi specialist (and other information on the list)
indicated that the repeated failure of cylinders was most
likely caused by excessive pedal pressure required to push
the clutch in, so it might need the standard full clutch job
with new friction components and lubrication. Other failure
can be precipitated if this is left unheeded, such as the
pedal *breaking off*!
Learn from our mistakes. Please.